1. Field of the Invention
The present invention relates to a shock absorber for an automotive suspension system. More specifically, the invention relates to a seal structure for a shock absorber for preventing a gaseous state working fluid in a fluid reservoir from leaking into a working chamber.
2. Description of the Background Art
Japanese Patent First (unexamined) Publication (Tokkai) Showa 58-156739 discloses a shock absorber which has coaxially defined inner and outer cylinders defining a fluid reservoir chamber in which hydraulic working fluid and pneumatic working fluid are filled, which fluid reservoir chamber is defined between the inner and outer cylinders. The disclosed shock absorber has a path for establishing a working chamber filled with a hydraulic working fluid and a the fluid reservoir chamber. A seal structure is provided in the path for permitting the hydraulic fluid from the working chamber to the fluid reservoir and blocking pneumatic fluid flow from the fluid reservoir to the working chamber.
In the conventional construction of the seal structure for such a type of the shock absorber, a seal member is provided for permitting and blocking fluid communication. Namely, in general, the hydraulic fluid pressure in the working chamber is higher than the pneumatic fluid pressure in the fluid reservoir chamber, and, alternatively, in the piston rebounding stroke, the pneumatic pressure in the fluid reservoir becomes higher than the hydraulic fluid pressure in the working chamber. Therefore, in the usual construction of the seal structure as disclosed in the Japanese patent First Publication 58-156739, one or more grooves are formed on the seal member so tat part of hydraulic working fluid in the working chamber can flow into the fluid reservoir only in the piston bounding stroke.
In such conventional seal structure, various drawback have been encountered. For example, when the seal member establishes the gas tight seal by face-to-face contact with a constructional seat member to seat thereof. Substantially high surface accuracy of the mating surfaces of the seal member and the seat member are required On the other hand, when the seal member is formed of a resin material, wearing of the resin seal member will cause leakage of the pneumatic working fluid into the working chamber to cause aeration.